To weld tubes to a tube sheet, particularly in making heat exchangers constituted by a great number of tubes the ends of which engage in orifices pierced in a tube sheet, an automatic welding head is generally used, comprising a torch and means for displacing the torch in several directions to allow it to follow each contour to be welded, one after the other.
There are various systems of welding, but the automatic stage of the method is most often limited to welding of a single contour. An operator must therefore set the welding head over the tube to be welded and place the torch on the starting point for the first bead, then strike the arc, welding then being carried out by automatic displacement of the torch along the contour to be welded. When welding is completed, it is usual to go past the starting point so as to obtain an overlap. The operator then stops the torch and switches off the arc, then positions the welding head on the next tube. The operator is thus obliged to intervene at the end of the welding of each bead in order to place the welding head over the next tube and position the torch at the starting point of the new bead to be welded. This operation is tricky and lengthy. The arc must also be struck and then switched off at the end of the bead, each time a bead is made. These transitory stages are difficult to monitor and can involve local faults, protuberances due to striking flash or microcraters when the arc is extinguished.
There is also a known method of continuous welding which consists in placing plugs in all the tubes, allowing simple welding passes to be made over the whole of the sheet, the tubes then being rebored. This method considerably increases the length of the weld beads and necessitates machining afterwards.
The object of the invention is a new method of welding allowing these problems to be solved by effecting continuous and automatic welding.